Electric circuit breakers

ABSTRACT

The invention concerns a fluid-immersed electric circuit breaker comprising first an second sets of fixed contacts each said set comprising a fixed main contact and a fixed arcing contact, an insulating carrier structure, a movable bridging contact carried on said insulating carrier structure and having first and second sets of movable contacts each set comprising a movable main contact and a movable arcing contact, said movable main and arcing contacts being movable to engage respective ones of said fixed main and arcing contacts, a fluid-filled arc-quenching chamber housing said movable contact sets and having a restricted outlet positioned so that under pressure of gas generated by arcing within the chamber a stream of said fluid under pressure is directed across an arcing path between one of said fixed arcing contacts and the associated one of said movable arcing contacts. In accordance with the invention the said arcing path is surrounded by at least one loop of ferromagnetic material which has been found to improve quenching of the arc.

United States Patent Caton [451 Oct. 17,1972

[541 ELECTRIC CIRCUIT BREAKERS [72] Inventor: George Caton, Ilkley, England [73] Assignee: Yorkshire Switchgear and Engineering Co., Limited, Leeds, Yorkshire, England [22] Filed: Oct. 18, 1971 [21] App1.No.: 189,879

[30] Foreign Application Priority Data Primary Examiner-Robert S. Macon Attorney-Richard K. Stevens et a1.

[57] ABSTRACT The invention concerns a fluid-immersed electric circuit breaker comprising first. an second sets of fixed contacts each said set comprising a fixed main contact and a fixed arcing contact, an insulating carrier structure, a movable bridging contact carried on said insulating carrier structure and having first and second sets of movable contacts each set comprising a movable main contact and a movable arcing contact, said movable main and arcing contacts being movable to engage respective ones of said fixed main and arcing contacts, a fluid-filled arc-quenching chamber housing said movable contact sets and having a restricted outlet positioned so that under pressure of gas generated by arcing within the chamber a stream of said fluid under pressure is directed across an arcing path between one of said fixed arcing contacts and the assurrounded by at least one loop of ferromagnetic material which has been found to improve quenching of the arc.

10 Claims, 3 Drawing Figures PATENIEUom 11 1912 Sam 1 or 3 PATENTED T 17 SHEET 2 OF 3 PATENTEDUET 11 1972 SHEEI 3 [IF 3 ELECTRIC CIRCUIT BREAKERS This invention relates to fluid-immersed electric circuit breakers provided with arc-quenching means.

Electric circuit breakers are known having a movable bridging contact cooperating with a pair of fixed contacts to make and break a circuit between the fixed contacts. The bridging contact is carried by an insulating carrier structure, and for each fixed contact the ridging contact has a contact set comprising a movable main contact and a movable auxiliary arcing contact electrically connected to each, the two contact sets being electrically connected. The movable main and auxiliary contacts cooperate respectively with a main contact and an auxiliary arcing contact together making up the fixed contact. When all contacts are closed a connection between each contact set and its associated fixed contact is made through parallel paths across the main contacts and the auxiliary arcing contacts. The arrangement is such that the arcing contacts are arranged to break this connection after the main contacts, and to make the connection before the main contacts, so that arcing is confined to the arcing contacts. These arcing contacts are housed in an arc-quenching chamber filled with a fluid suitable for arc-quenching purposes, a commonly used fluid being oil. The arcing contacts of both contact sets are housed in a common arc-quenching chamber, and the arrangement is usually such that the arcing contacts associated with one fixed contact are caused to arc before those of the other fixed contact, so generating gas, the pressure of which forces a stream of fluid across the arcing path of the other fixed contact to a restricted outlet from the arc-quenching chamber to assist in quenching the arc.

The object of the present invention is to provide improved arc quenching in a circuit breaker of this type.

According to the present invention a fluid-immersed electric circuit breaker includes a pair of fixed contacts each comprising main contacts and arcing contacts, a movable bridging contact carried on an insulating carrier structure and having two sets of movable main and arcing contacts, the movable main and arcing contacts of each set being movable to engage respectively the main and arcing contacts of a respective one of the fixed contacts, the movable arcing contacts being disposed in an arc-quenching chamber having a restricted outlet positioned so that under pressure of gas generated by arcing within the chamber a stream of fluid under pressure is directed across the arcing path between at least one pair of fixed and movable arcing contacts, and one or more of the arcing paths being surrounded by at least one loop of ferromagnetic material.

When arcing takes place due to the parting of the arcing contacts in such a circuit breaker the arcing current induces eddy currents in the loop or loops of ferromagnetic material and produces a complex magnetic field of strength proportional to the arcing current.

This field includes loops closely surrounding the arc path and each loop acts to constrict the arc toward the minimum path between the fixed and movable arcing contacts. Furthermore, the complex interacting fields created by this multiplicity of loops during the movement of the bridging contact cause a rapid oscillatory disturbance of the arc within the path and produces considerable oil and gas turbulence within the region in and around the arc path. This turbulence assists in cooling the arc and also contributes towards the instability of the arc so that it is more sensitive to de-ionization by the stream of fluid directed across the path of the arc. The arc is therefore quenched more easily than with existing circuit breakers. Accordingly a given arcing current can be handled by a smaller circuit breaker than is used at the moment, or conversely a circuit breaker according to the invention of comparable dimensions to a conventional circuit breaker will be able to handle a higher arcing current at the same or at a higher voltage than the conventional circuit breaker.

Preferably the circuit breaker-is such that arcing occurs over a first pair of fixed and movable arcing contacts before arcing occurs over the second pair of fixed and movable arcing contacts, and the arc-quenching chamber is shaped so that the gas generated at the first pair of arcing contacts directs a stream of oil across the arcing path between the second pair of arcing contacts, each pair of arcing contacts being surrounded by a closed loop or loops of ferromagnetic material.

It would alternatively be possible to provide the ferromagnetic material only around the second pair of arcing contacts.

Although a single loop round each pair of arcing contacts may be used, it is desirable to provide two or more loops. Preferably all the loops associated with a pair of arcing contacts have a common ferromagnetic member or are externally joined together by ferromagnetic members. These features increase the complexity and cross-sectional area of the magnetic field about the are further to assist control of the arc. The complexity of this field may be still further increased by increasing the cross-sectional area of the external path by providing a further ferromagnetic member joining together the loops associated with the two spaced pairs of arcing contacts.

All or any of the loops of ferromagnetic material may be either closed or open, i.e. the ferromagnetic path around the arc may be continuous or it may be interrupted by one .or more gaps. The invention is effective as long as there is sufficient ferromagnetic material to enable the arcing current to induce a magnetic field affecting the stability of the arc.

Movable bridging contact assemblies, conventionally known as arc traps, for circuit breakers of the type'with which the invention deals provide two movable contact sets, each contained by a laminar structure, usually including outer conductive plates constituting the movable main contacts, insulating layers to the insides of these plates and laminations of fiber or other are resistant material to the inside of the insulating layers, there being a space in the laminar structure to receive the fixed arcing contacts. The movable arcing contacts are housed between, and conductively connected to, the outer conductive plates.

This structure does not have a great deal of inherent strength and the short circuit rupturing capacity of the entire circuit breaker has often been limited by the bursting strength of the laminar movable assembly. According to a further feature of the invention the ferromagnetic loop associated with a laminated structure movable contact assembly comprises ferromagnetic strips to the outside of the outer conductive plates, the ferromagnetic strips being joined by ferromagnetic bolts passing transversely through the laminations of the arc trap assembly. The bolts can be made quite heavy and they are found to increase the bursting strength of the movable contact quite considerably. It is possible to use two bolts, one to each side of the arcing path to form a closed loop around this, but preferably two or more pairs of bolts are provided passing through the laminated structure at different levels. This both increases the cross-sectional area of the magnetic path or loop and increases the bursting strength of the arc trap assembly.

Steel strips and bolts have been found to be preferable, but other ferromagnetic materials may be employed.

An example of a circuit breaker according to the invention will now be described in more detail with reference to the accompanying drawing in which:

FIG. 1 is a section through the center line of the movable bridging contact of the circuit breaker;

FIG. 2 is a section on the line A-A of FIG. 1; and

FIG. 3 shows a part section of a fixed contact of the circuit breaker with part of the bridging contact in the closed position.

The circuit breaker comprises a movable bridging contact 1 carried by an insulating carrier structure 2 and cooperating with a pair of fixed contact assemblies 3 and 4 to make and break a circuit. Each fixed contact assembly has a main contact comprising copper fingers 5 and 6 and an auxiliary arcing contact in the form of an elongated electrode 7 which may have a tungsten copper tip.

The bridging contact comprises two similar contact sets la and 1b, and only contact lawill be described in detail. This comprises two outer copper conducting plates 8 and 9 constituting a main contact, further conducting plates 10 and 11, insulating plates 12 and 13 and fiber arc trap plates 14 and 15 which are shaped to form space 16 to accept the electrode 7. The plates 14 and 15 are also shaped to accept arcing contacts 17 and 18 electrically connected to plates 8 and 9 by conductors 19 and 20. This laminated structure is held together by steel plates 21 and 22 outside the copper plates 8 and 9 and bolts 23 to 27 extending between the plates so that the plates and bolts together form a closed loop of ferromagnetic material around the arcing contacts 17 and 18.

The arcing contacts 17 and 18 of the contact set la lie at one end of an arc-quenching chamber 29, and the arcing contacts of the other contact set lb lie at the other end of the arc quenching chamber. The chamber is filled with oil, and has passages 30 to 33 for passage of oil. Passages 32 and 33 intersect the line of an arc struck between electrode 7 of fixed contact 4 and arc ing contacts 17 and 18 of contact set 1a.

The arrangement of the contacts is such that when the circuit is to be broken the main contacts such as 5 and 6 of both fixed contacts leave the main contacts-8 and 9 of the respective movable ridging contact set before the arcing contacts of the movable and fixed contacts part. Arcing contacts at fixed contact 3 part before those at fixed contact 4, so that the arc produced at contact 3 generates gas which forces gas and oil in chamber 29 out through ports 32 and 33. This movement of the oil occurs as the arcing contacts at fixed contact 4 part, and the moving gas and oil extinguishes the arc over these contacts to break the circuit. As already made clear, the constriction of the arc by the magnetic field due to the ferromagnetic side plates and bolts, and the instability of the arc render quenching of the are by the flow of gas and oil easier than it would be were the magnetic field not present.

The bolts 23 to 27 impart bursting strength to the movable contacts 1a and 1b so that the circuit breaker can withstand substantial pressures.

A ferromagnetic plate 34 joins together the ferromagnetic loops associated with the contact sets 1a and 1b.

What I claim is:

1. A fluid-immersed electric circuit breaker comprising first and second sets of fixed contacts each said set comprising a fixed main contact and a fixed arcing contact, an insulating carrier structure, a movable bridging contact carried on said insulating carrier structure and having first and second sets of movable contacts each set comprising a movable main contact and a movable arcing contact, said movable main and arcing contacts being movable toengage respective ones of said fixed main and arcing contacts, a fluid-filled arc-quenching chamber housing said movable contact sets and having a restricted outlet positioned so that under pressure of gas generated by arcing within the chamber a stream of said fluid under pressure is directed across an arcing path between one of said fixed arcing contacts and the associated one of said movable arcing contacts, and at least one loop of ferromagnetic material surrounding said arcing path.

2. A circuit breaker as claimed in claim 1 which is such that arcing occurs between said fixed and movable arcing contacts of said first contact sets before arcing occurs between said fixed and movable arcing contacts of said second contact sets, and said arc-quenching chamber is shaped so that gas generated during arcing at said first contact sets directs a stream of said fluid across the arcing path at said second contact sets, said arcing contacts in each contact set being surrounded by a closed loop or loops of ferromagnetic material.

3. A circuit breaker as claimed in claim 1 wherein at least two closed loops of ferromagnetic material are provided surrounding said arcing path.

4. A circuit breaker as claimed in claim 3 wherein all said closed loops have a common ferromagnetic member.

5. A circuit breaker as claimed in claim 3 wherein all said closed loops are externally joined together by ferromagnetic members.

6. A circuit breaker as claimed in claim 2 and including a further ferromagnetic member joining together said loops surrounding said arcing contacts in each contact set.

7. A circuit breaker as claimed in claim 1 wherein said at least one loop of ferromagnetic material includes at least one closed loop.

8. A circuit breaker as claimed in claim 1 wherein said at least one loop of ferromagnetic material includes at least one open loop.

9. A circuit breaker as claimed in claim 1 and including laminar arc trap structure each containing one of said sets of movable contacts, each said laminar arc trap structure comprising outer conductive plates constituting said movable main contacts, insulating layers to the insides of said outer conductive plates, and

laminations of are resistant material to the inside of said insulating layers, wherein said ferromagnetic loop associated with said arcing contacts of each set comprises ferromagnetic strips to the outside of said outer conductive plates and ferromagnetic bolts joining said ferromagnetic strips and passing transversely through 

1. A fluid-immersed electric circuit breaker comprising first and second sets of fixed contacts each said set comprising a fixed main contact and a fixed arcing contact, an insulating carrier structure, a movable bridging contact carried on said insulating carrier structure and having first and second sets of movable contacts each set comprising a movable main contact and a movable arcing contact, said movable main and arcing contacts being movable to engage respective ones of said fixed main and arcing contacts, a fluid-filled arc-quenching chamber housing said movable contact sets and having a restricted outlet positioned so that under pressure of gas generated by arcing within the chamber a stream of said fluid under pressure is directed across an arcing path between one of said fixed arcing contacts and the associated one of said movable arcing contacts, and at least one loop of ferromagnetic material surrounding said arcing path.
 2. A circuit breaker as claimed in claim 1 which is such that arcing occurs between said fixed and movable arcing contacts of said first contact sets before arcing occurs between said fixed and movable arcing contacts of said second contact sets, and said arc-quenching chamber is shaped so that gas generated during arcing at said first contact sets directs a stream of said fluid across the arcing path at said second contact sets, said arcing contacts in each contact set being surrounded by a closed loop or loops of ferromagnetic material.
 3. A circuit breaker as claimed in claim 1 wherein at least two closed loops of ferromagnetic material are provided surrounding said arcing path.
 4. A circuit breaker as claimed in claim 3 wherein all said closed loops have a common ferromagnetic member.
 5. A circuit breaker as claimed in claim 3 wherein all said closed loops are externally joined together by ferromagnetic members.
 6. A circuit breaker as claimed in claim 2 and including a further ferromagnetic member joining together said loops surrounding said arcing contacts in each contact set.
 7. A circuit breaker as claimed in claim 1 wherein said at least one loop of ferromagnetic material includes at least one closed loop.
 8. A circuit breaker as claimed in claim 1 wherein said at least one loop of ferromagnetic material includes at least one open loop.
 9. A circuit breaker as claimed in claim 1 and including laminar arc trap structure each containing one of said sets of movable contacts, each said laminar arc trap structure comprising outer conductive plates constituting said movable main contacts, insulating layers to the insides of said outer conductive plates, and laminations of arc resistant material to the inside of said insulating layers, wherein said ferromagnetic loop associated with said arcing contacts of each set comprises ferromagnetic strips to the outside of said outer conductive plates and ferromagnetic bolts joining said ferromagnetic strips and passing transversely through said laminar arc trap structure.
 10. A circuit breaker as claimed in claim 9 wherein at least two pairs of ferromagnetic bolts are provided passing through said laminar arc trap structure at different levels. 